The UK has been America's most reliable ally in Afghanistan during eight years of war, with the 9,000 British troops there now second only to the US contingent of about 65,000. But amid a debate in Washington over expanding the war, in which chief Afghan war planner General Stanley McChrystal is pushing for 40,000 more troops, the small size of the proposed British increase and the caveats Mr. Brown placed on it demonstrate that a large increase from other allies to match any new US commitment is unlikely.

Europe's standing armies are much smaller than that of the US. Britain, France, and Germany have collectively about 350,000 active duty soldiers. The US army has about 550,000.

European leaders, who by and large have remained supportive of the war even as polling shows most of their citizens are turning against it, are now waiting to see which way President Obama jumps on the troop request before taking new positions of their own.

Mr. Brown on Wednesday said Britain will up its troop total in Afghanistan to 9,500 provided the British military properly equips the soldiers, if more troops are recruited into the Afghan national army and if he sees that other NATO countries are "bearing their fair share" of the troop burden.

The first point, on proper equipment, reflects the political fire that Brown has taken for poor armor issued to troops and run-down helicopters and other equipment.

Currently the NATO Afghan operation has more than 100,000 troops (65,000 of them are American.) At the height of the Soviet occupation of Afghanistan, the Red Army had approximately 120,000 soldiers.

If Brown's announcement is designed to push Spain, France, and other European states to take a greater share of responsibility, 500 is no a rallying figure. Speculation in Paris ran to whether Brown is anteing up 500 troops now in order not to send a substantially higher number later or if they are being sent mainly to give rest to the current, exhausted British forces in southern Helmand province, where fighting with the Taliban has been fierce.

"The understanding in continental Europe is that we don't have an answer to a question that hasn't been posed," says Francois Heisbourg of the Foundation for Strategic Research in Paris. "Obama has still not made up his mind about what his strategy is. We aren't going to put the cart before the horse. American pressure on Europe won't work without an understanding of what we are doing in Afghanistan."

Sources in the German foreign ministry say that Germany has not been pressured by Washington for more troops; US diplomats said early in the Obama administration that he was aware that German chancellor Angela Merkel would not send further soldiers in an election year. Germany is currently the third largest contributor to the force, with about 4,500 troops in Afghanistan.